Low power modulation

Abstract

Performing low power modulation enabling a modulation scheme that conveys at least two bits of information using differential voltages having variable common mode voltage and using two voltage references and rejecting the common mode voltage.

What is claimed is:  
     
         1 . A method comprising: 
 enabling a modulation scheme that conveys at least two bits of information using differential voltages having variable common mode voltage and using two voltage references; and    rejecting the common mode voltage.    
     
     
         2 . The method of  claim 1  in which the common mode voltage has a non-zero value.  
     
     
         3 . The method of  claim 1  further comprising enabling an orthogonal modulation scheme in addition to the modulation scheme.  
     
     
         4 . The method of  claim 3  in which the orthogonal modulation scheme includes a width modulation scheme.  
     
     
         5 . The method of  claim 3  in which the orthogonal modulation scheme includes a rise-time modulation scheme.  
     
     
         6 . The method of  claim 1  in which the modulation scheme uses an additional voltage reference.  
     
     
         7 . The method of  claim 1  in which the differential voltages include a voltage pair in which one of the voltage pair voltages equals zero.  
     
     
         8 . The method of  claim 1  further comprising enabling the information to be used in an electromagnetically coupled multi-drop bus environment.  
     
     
         9 . An article comprising: 
 a machine-readable medium which contains machine-executable instructions, the instructions causing a machine to: 
 enable a modulation scheme that conveys at least two bits of information using differential voltages having variable common mode voltage and using two voltage references;  
 reject the common mode voltage.  
   
     
     
         10 . The article of  claim 9  in which the common mode voltage has a non-zero value.  
     
     
         11 . The article of  claim 9  further causing a machine to enable an orthogonal modulation scheme in addition to the modulation scheme.  
     
     
         12 . The article of  claim 11  in which the orthogonal modulation scheme includes a width modulation scheme.  
     
     
         13 . The article of  claim 11  in which the orthogonal modulation scheme includes a rise-time modulation scheme.  
     
     
         14 . The article of  claim 11  in which the modulation scheme uses an additional voltage reference.  
     
     
         15 . The article of  claim 11  in which the differential voltages include a voltage pair in which one of the voltage pair voltages equals zero.  
     
     
         16 . The article of  claim 11  further causing a machine to enable the information to be used in an electromagnetically coupled multi-drop bus environment.  
     
     
         17 . An apparatus comprising: 
 a transmitter configured to transmit differential voltages having variable common mode voltage;    a voltage generation mechanism configured to provide two voltage references to the transmitter; and    a receiver configured to receive the differential voltages and to perform a demodulation scheme that conveys at least two bits of information using the differential voltages.    
     
     
         18 . The apparatus of  claim 17  in which the transmitter is also configured to receive the voltage references from a source outside the apparatus.  
     
     
         19 . The apparatus of  claim 17  further comprising 
 an electromagnetically coupled bus, and  
 a zig-zag coupler associated with the electromagnetically coupled bus and configured to stabilize coupling coefficients associated with the differential voltages using a zig-zag coupler shape for transferring the differential voltages.  
 
     
     
         20 . The apparatus of  claim 17  further comprising 
 an electromagnetically coupled bus, and  
 a coupler associated with the electromagnetically coupled bus and configured to reduce translation of common mode noise to differential noise.  
 
     
     
         21 . The apparatus of  claim 17  in which the receiver is also configured to use a common mode rejection technique.  
     
     
         22 . A system comprising: 
 a bus;    a device;    an interface configured to use two voltage references to encode at least two bits to symbols for transmission from the bus to the device and to decode symbols to at least two bits for transmission to the bus from the device, the symbols including differential voltages having variable common mode voltage.    
     
     
         23 . The system of  claim 22  in which the bus includes a multi-drop bus.  
     
     
         24 . The system of  claim 22  in which the interface includes an electromagnetic coupler.  
     
     
         25 . The system of  claim 22  in which the interface is also configured to reject the common mode voltage.  
     
     
         26 . A method comprising: 
 providing a first voltage at a first voltage level;    providing a second voltage at a second voltage level different from the first voltage level, the first voltage level and the second voltage level having a variable common mode voltage;    coding at least two bits of data using two voltage references and using a difference between the first voltage level and the second voltage level; and    rejecting the common mode voltage.    
     
     
         27 . The method of  claim 26  further comprising 
 providing a third voltage at a third voltage level,  
 providing a fourth voltage at a fourth voltage level different from the third voltage level, the third voltage level and the fourth voltage level having a variable common mode voltage, and  
 coding the data also using a difference between the third voltage level and the fourth voltage level.  
 
     
     
         28 . The method of  claim 26  further comprising 
 providing at least one additional pair of voltages, each pair including two voltages at different voltage levels and having a variable common mode voltage, and  
 coding the data also using differences between the voltage levels of each of the pairs.  
 
     
     
         29 . The method of  claim 26  further comprising transmitting the data between a device and an electromagnetically coupled bus.